The Taoiseach says he's "deeply sorry" for the State's failings in the Stardust tragedy.
Simon Harris has made a 25-minute speech in the Dáil, where he named each of the 48 victims and said something personal about them.
Relatives and survivors were present in the visitors' gallery to witness the State apology.
The Taoiseach says the families were forced into a living nightmare.
Simon Harris met some of the relatives at his offices in Government Buildings on Saturday, and families have been gathering at Leinster House to hear the State apology since earlier this morning.
It comes after the family’s 43-year fight for justice resulted last week in a verdict of unlawful killing at the inquests into their deaths.
"Living Nightmare"
Simon Harris said the State and its instructions failed each of them: "I know that you were forced to endure a living nightmare which began when your loved ones were so cruelly snatched from you in a devastating fire.
"Their unfinished stories became you story, the defining story of your lives.
"I am deeply sorry that you were made to fight for so long that they went to their graves never knowing the truth.
"Today we say formally and without any equivocation, we are sorry. We failed you when you needed us the most.
"From the very beginning, we should have stood with you, but instead we forced you to stand against us.
"48 young people lost their lives in the Stardust disaster - many more were injured and even more still had their lives broken and shattered forever.
Mr Harris said he hopes today can bring families "in from the cold and end the neglect of 43 years waiting and fighting for the only thing you ever wanted: the truth.
"I hope this is a moment when the State, which rubbed salt in your terrible wounds, starts to help you heal.
"They were bright, beautiful people. They had plans and dreams, their whole lives ahead of them.
Apology
He then read out the names of those killed in the early hours of Valentine's Day in 1981, before saying: "It is to our great and eternal shame that far from the warm embrace of a caring State, the Stardust families experienced a cold shoulder, and a deaf ear and two generations of struggle for truth and justice.
"Instead, it is to our great shame that State processes heaped misery upon tragedy for the Stardust families.
"I am so deeply sorry your first bid for justice ended with suspicion being cast on those who had died or survived on that catastrophic night.
"For all of this, as Taoiseach, on behalf of the State, I apologise unreservedly to all the families of the Stardust victims and all the survivors for the hurt that was done to them and for the profoundly painful years of struggle for the truth".
